Security apparatus



June 24, 1969 F" D. BROOKS 3,451,708

SECURITY APPARATUS Filed Dec. 4, 1968 F E L TON D. BROOKS /N VIE N TOR iww ATTORNEY United States Patent U.S. Cl. 292--264 3 Claims ABSTRACT OFTHE DISCLOSURE In the representative embodiments of the inventiondisclosed herein, a metal loop adapted to pass over a door knob iscoupled to a stout connecting member of limited length for allowing thedoor to be only partially opened when the loop is fitted over the doorknob. By selectively designing the loop to yield without failing underforce, an attempted illegal entry of a door or window secured by thepresent invention will be safely resisted by the controlled deform on ofthe loop which absorbs such sudden impacts as well as provides anindication of the attempted entry.

This apparatus is a continuation-impart of US. application Ser. No.661,351, filed Aug. 17, 1967, now abandoned.

Various arrangements of safety chains and the like have, of course, beenemployed heretofore as a security measure to enable doors and windows tobe only partial- 1y opened without risking an unwanted intrusion or asurreptitious disconnection of the security chain. Most, if not all, ofthe security latches of this nature are, however, generally much stouterthan the screws or other fasteners used for attaching them. Thus,although these fasteners may well withstand a relatively steady force,the fasteners typically used will often be jerked out of the door orwindow frame by sudden impacts. It will also be realized that unless anattempted entry results in physical damage to the woodwork, an attemptedentry could well be unnoticed.

Accordingly, it is an object of the present invention to provide new andimproved entry-restraining apparatus adapted to withstand sudden impactsas well as to provide a reliable indication of an unsuccessful forcibleentry.

This and other objects of the present invention are attained byproviding entry-restraining apparatus adapted to releasably latch a dooror window to its associated framework and including a loop or ringhaving a selected limited yield strength. By securing the loop betweenthe door or window and framework, sudden impacts attempting to forciblyopen the door or window will only controllably deform the loop to atleast partially absorb the impact. Moreover, a surreptitious attempt toforce the door or window will deform the loop so as to provide a warningindication that the attempt had been made.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary apparatus and methods employingthe principles of the invention as illustrated in the accompanyingdrawings, in which:

FIGURE 1 illustrates one embodiment of the present invention especiallyadapted for releasably latching a single door; and

FIGURE 2 depicts an alternate embodiment of the present inventionespecially adapted for releasably latching oppositely-swinging doubledoors.

Turning now to FIGURE 1, entry-restraining apparatus 10 incorporatingthe principles of the present invention is shown in position forreleasably latching a typical single door 11. -In the preferred formillustrated, the entry-restraining apparatus 10 is comprised of a ring12 that is detachably interconnected between the door 11 and itsassociated frame 13 by a short length of a stout cable or chain 14. Tosecure the chain 14, its free end is coupled to the adjacent door frame13 by means such as a typical bracket 15 fastened to the frame by boltsor screws 16 of adequate length. The other end of the chain 14 is, ofcourse, connected to the ring 12 in a suitable manner.

It will be appreciated from the drawings that the ring 12 isappropriately sized to facilitate its placement over a projection on thedoor 11 such as a typical door knob 17. Thus, by suitably proportioningthe length of the chain 14 and diameter of the ring 12, the door 11cannot be opened more than a few inches once the ring is disposed overthe door knob 17. This will, of course, permit the door to be safelyopened without fear that an intruder might attempt to force the doorfurther open. Similarly, by limiting the free travel of the door 11 inthis manner, the chain 114 is so short that the ring 12 cannot beremoved [from the knob 17 unless the door is at least nearly closed.

To accomplish the objects of the present invention, the ring 12 isselectively designed to yield or deform without breaking under a tensileload that might be expected to be applied to the ring by one attemptingto make a forcible entry through the door '11. In this manner, should anintruder attempt to lunge at the door 11 while it is partially ajar, asubstantial portion of the impact against the door will be absorbed asthe ring 12 is elongated. Accordingly, instead of imposing a suddenimpact against the screws 16 which might possibly rip them from the doorframe 13, the controlled deformation or elongation of the ring 12 willdissipate a substantial proportion of the impact. Thus, a frightenedoccupant would be given sufiicient time to quickly slam the door 11before another attempt could be made to force an entry.

An added benefit provided by the selective deformational characteristicof the ring 12 is that an undetected surreptitious attempt to force thedoor 11 simply cannot be made if sufficient force is applied to deformthe ring. Thus, even though such an attempt is foiled, the permanentdeformation of the ring 12 will be mute testimony that an unlawful entryhad been attempted; and even though the occupant is absent, thedeformation of the ring 12 will give a clear warning that anotherattempt might again be made. Thus, in addition to having a policeinvestigation, the occupant can also take appropriate preventativesteps.

Turning now to FlGURE 2, an alternate embodiment 20 of the invention asillustrated is shown for releasably latching a pair ofoppositely-swinging double doors 21 and 22. As seen there, thisalternate security apparatus 20 is comprised of a pair of loops or rings23 and 24 respectively fitted loosely over the knobs 25 and 26 of thedoors 21 and 22 and interconnected by a short length of a stout cable orchain 27. Although only one or the other of the two rings 23 and 24 needto be selectively deformable, it is preferred that both be capable ofdeformation. Accordingly, it will be appreciated that an attempt toforce either or both of the doors 21 and 22 will be effectively resistedin the same manner as previously described and, of course, with similarresults.

To determine the physical dimensions as well as the choice of materialfor the rings 12, 23 or 24, convention'al strength of material formulasare used to assure that the rings will readily deform without breakingunder a selected load. In calculating the properties of a selected ring,it will be appreciated that it is primarily the bending moment imposedby the forces on the ring that will cause its deformation. In otherwords, upon application of force thereto, the bending moment mustdevelop a stress in excess of the allowable yield stress of the selectedmetal. Once it is determined that a selected ring will deform under agiven load, a determination is then made to be certain that the designload will not cause breaking of the ring. if both conditions are met,the selected ring will be suited for use in the present inveniton. 'Itshould also be noted that, if desired, a ring can be notched slightly toachieve a specific design.

These two conditions may, of course, be determined either by testing orby calculation from formulas found in any standard work on strength ofmaterials. On typical formula is found in -Roark, Formulas for Stressand Strain (2d. ed. 1943), Table 8, page 152:

M =0.3183 WR (Equation 1) where:

M =bending moment, in.-lbs.

W=load, lbs.

\R=radi-us from center of ring to central axis of metal,

inches.

The ring is then checked for strength in tension by the usual formula:

S =W/ 2a (Equation 3) where:

S =tensile stress, p.s.i.

W=load, lbs. a=cross-sectional area of tranverse section of ring, in.

In a typical embodiment of the present invention, a ring (as at 12 inFIGURE 1) was designed for a load of ISO-lbs. Using A-36 steel for thering of y -inch diameter material, and formed into a ring having adiameter of 2 -inches between center lines of metal section (FA-inchesinside diameter), calculations and tests showed the ring would reliablydeform under a load of ISO-lbs. but was still well below the breakingpoint. Accordingly, with this ring as at 12 or 23 and 24, it will beappreciated that an attempt to force open a door or window will succeedonly in deforming the ring. Thus, by selectively controlling thestrength of these rings 12, or 23 or 24, an attempted illegal entry of adoor or window secured by the security apparatus of the presentinvention will be safely resisted by the controlled deformation of therings which will absorb sudden impacts as well as provide indicationsthat such an entry had been attempted.

What is claimed is:

1. Apparatus adapted for selectively restraining a door operatively hungin an opening in a wall and comprising: a closed metal ring adapted topass over a door knob and having a uniform transverse circularcross-section selected in accordance with the yield strength andultimate strength of said metal so that, upon application to said ringof opposed forces less than a predetermined magnitude, said ring willpermanently elongate and at least partially collapse; a chain coupled tosaid ring and of a strength to carry tensile forces in excess of saidpredetermined magnitude; and means on said chain adapted for connectionto an adjacent wall to limit the opening travel of a door hung thereinto a specified distance whenever said ring is on a knob on that door.

2. The apparatus of claim 1 wherein said connection means include asecond closed metal ring adapted to pass over a knob on a second dooroperatively hung in such an opening adjacent to the first-mentioneddoor.

3. The apparatus of claim 2 wherein said second metal ring is identicalto said first-mentioned metal ring.

References Cited UNITED STATES PATENTS 878,607 2/1908 Cairns 292-2641,744,456 1/ 1930 Ellingson 292264 X 2,199,369 4/1940 Bernstein 292262 X2,662,571 12/ 1953 Kessler 292264 X MARVIN A. CHAMPION, PrimaryExaminer.

E. I. MCCA'RTHY, Assistant Examiner.

